Stabilized construction wall in unstable footing

ABSTRACT

An arrangement for providing stabilization for a construction wall during construction in an unstable footing which includes the formation of a basin above the pre-existing surface level of a proposed construction zone or site. The basin is used to receive fluid therein to provide increased hydrostatic pressure, acting on the wall from inside the construction site to provide pressure within the site to a degree approximating the countervailing pressures acting on the construction wall from outside the site. Then, while maintaining the hydrostatic pressure, the soil materials within the site are removed by excavating down to a predetermined level and replaced (while still maintaining the hydrostatic pressure) with a stabilizing fill material of greater strength than the unstable material removed from the site. Thereafter, the hydrostatic pressure can be relieved and preparation of the site continued. The wall structure formed will ultimately be characterized by an unstable footing material on one side of the wall at the lower end thereof, a mat of stable footing material on the other side of the wall, and a mat of concrete superimposed upon the mat of stabilized footing material so that the concrete mat can counteract laterally acting forces pressing against the outside of the wall.

Ger-wick, Jr.

[ 51 June 6, 1972 STABILIZED CONSTRUCTION WALL IN UNSTABLE FOOTING lnventor: Ben C. Gerwick, Jr., Oakland, Calif.

Assignee: J. H. Pomeroy & Co., Inc., San Francisco,

Calif.

Filed: May 15, 1970 Appl. No; 37,747

Related [1.8. Application Data [62] Division of Ser. No. 811,331, Mar. 28, 1969, Pat. No.

[52] U.S.CI ..61/39 [51] Int. Cl. ..E02d 3/12, E02d 5/18, E02d 27/04 [58] Field of Search ..52/169, 292, 742; 61/35, 39, 61/49, 50

[56] References Cited UNITED STATES PATENTS 2,101,358 12/1937 Boardman ..61/50 1,049,221 12/1912 Frankignoul ..61/50 2,960,745 11/1960 Wallace ...6l/50 3,490,242 1/1970 Schnabel ..61/39 Primary ExaminerDavid J. Williamowsky Assistant Examiner-David H. Corbin AtlorneyFlehr, Hohbach, Test, Albritton & Herbert 57] ABSTRACT An arrangement for providing stabilization for a construction wall during construction in an unstable footing which includes the formation of a basin above the pre-existing surface level of a proposed construction zone or site. The basin is used to receive fluid therein to provide increased hydrostatic pressure, acting on the wall from inside the construction site to provide pressure within the site to a degree approximating the counter-vailing pressures acting on the construction wall from outside the site. Then, while maintaining the hydrostatic pressure, the soil materials within the site are removed by excavating down to a predetermined level and replaced (while still maintaining the hydrostatic pressure) with a stabilizing fill material of greater strength than the unstable material removed from the site. Thereafter, the hydrostatic pressure can be relieved and preparation of the site continued. The wall structure formed will ultimately be characterized by an unstable footing material on one side of the wall at the lower end thereof, a mat of stable footing material on the other side of the wall, and a mat of concrete superimposed upon the mat of stabilized footing material so that the concrete mat can counteract laterally acting forces pressing against the outside of the wall.

1 Claims, 10 Drawing Figures PATENTEUJUN 6 I972 3 687, 238

sum 1 (IF 2 INVENTOR. BEN C. GERWICK JR.

ATTORNEYS EI'LFLJ L 1 Fl [1 PATENTEnJu'n s 1912 3.661238 sum 2 or 2 W V F L BEN C. GERWICK JR.

4/ KZU WZW ATTORNEYS STABILIZED CONSTRUCTION WALL IN UNS'I' ABLE FOOTING CROSS-REFERENCE TO RELATED APPLICATION This application is a division of U.S. Ser. No. 81 1,331, entitled METHOD FOR CONSTRUCTING STABILIZED CON- STRUCTION WALL IN UNSTABLE FOOTING, filed Mar. 28, 1969, now U.S. Pat. No. 3,563,044.

BACKGROUND OF THE INVENTION This invention pertains to wall constructions and methods of stabilizing same in soil conditions where the footing is highly unstable, and more particularly in this division of the above referenced application to the stabilized wall.

In the construction of a building, foundation walls which extend down to a predetermined depth in unstable soil conditions, e.g., where the soil is somewhat fluid or marshy or otherwise unstable, as in a swamp or the like, may fail to encounter a proper footing of stable material. Without a stable footing during excavation of the construction site, it will be readily apparent that the load of earth pressure on the exterior surfaces of the wall can readily force the lower portion of the wall inwardly toward the construction site as support is removed from the construction wall within the excavation site. However, when the bottom end of the wall is embedded in a stable soil condition, the excavation can proceed without undue concern for the problems of the increasing pressures developing against the wall on the outside of the excavation site.

As disclosed herein, a wall structure is provided by a method which serves to stabilize the footing of an upright diaphragm wall structure of a type found commonly encircling a construction site.

Where the footing material is quite stable, the passive resistance of the material within the excavation site will ordinarily be sufficient to counter balance the pressures acting against the exterior of the wall surfaces.

In many instances, temporary struts have been jacked against the wall to insure a proper force counteracting the outside pressures bearing against the wall.

However, in highly unstable footing conditions, where the passive resistance is quite low, the present invention provides supporting forces acting from within the excavation site in a controlled manner to approximate the pressures acting from outside the excavation site.

SUMMARY OF THE INVENTION AND OBJECTS Thus, in general, pursuant to a preferred method of con struction as described below, there is provided a wall structure in an unstable footing wherein an upright diaphragm wall is arranged in the unstable footing material in a manner whereby the unstable material is on one side of the wall at the lower end of the wall while a mat of stable footing material is on the other side of the wall. On the mat of stable material, a concrete mat is superimposed which serves to counteract laterally acting forces pressing against the outside of the wall tending to force the bottom end of the wall inwardly toward the excavation.

In general, a preferred method has been provided for stabilization of a construction wall in an otherwise unstable footing material comprising the steps of forming a basin on top of the surface of a proposed construction zone or site. The basin has a predetermined depth and substantially fluid-impervious side wall boundaries including the upright wall structure which is to be stabilized. Thus, the wall to be stabilized also serves to define at least a portion of the boundaries of the site. Then, the hydrostatic pressure acting on the wall from inside the construction site or zone is increased to a degree approximating the countervailing pressure acting on the wall from outside the zone. This is accomplished, preferably, by the more particular steps of filling the basin with fluid material having a greater density than water so as to increase the hydrostatic pressure on the inside of the wall for countering the pressure acting on the outside of the wall. Then, while maintaining the increased pressure, the method contemplates removing the soil materials of the construction site down to a predetermined level while replacing the removed materials with a stabilizing fill material of greater strength. Thereafter, the applied hydrostatic pressure is removed to permit completion of construction by excavating and providing a concrete mat overlaid upon a pad of stable fill.

The degree of hydrostatic pressure employed within the site will, of course, vary with the passive resistance of the footing material within the site and also with the placement and use of strut supports.

In general, it is an object of the present invention to provide an improved stabilized wall construction in an unstable footmg.

The foregoing and other objects of the invention will be more clearly apparent from the following detailed description of preferred embodiments of the invention when considered in conjunction with the drawings.

I DESCRIPTION OF THE DRAWINGS FIGS. 1-8 are schematic side elevation section views show- I ing a sequence of steps incorporated in the preferred method of constructing a stabilized wall, FIG. 8 showing a fully stabilized wall, according to the invention;

FIG. 9 and FIG. 10, respectively, are plan views of two different construction sites utilizing the method according to the invention.

DESCRIPTION OFTI-IE PREFERRED EMBODIMENT Where excavation is to take 'place on one side of a construction wall while the other side of the wall remains subject to the earth pressures acting against the wall, it is readily apparent that the footing into which the wall is embedded must be sufficiently firm to hold the wall at the lower end thereof and prevent the pressure on the unexcavated side from forcing the bottom of the wall into the excavation whereby support of the earth is lost.

By the procedure now to be described, it is possible to provide a stabilized construction wall where the lower end of the wall will be properly supported against forces otherwise acting to move the bottom of the wall into the excavation. The procedure as describedherein further properly stabilizes the wall but in a manner whereby the bottom of the wall is not, on the other hand, forced outwardly away from the excavation zone.

Referring to the drawings, FIGS. l-8 represent a sequence of steps which are pursued to provide stabilization to a construction wall disposed upright in an unstable footing, such as may be found, for example, in a marsh, river bed, or bay bottom or other extremely weak soil condition.

Preliminarily, depending upon site conditions, the construction zone is graded in the region 11, as necessary, to provide a relieved outer margin disposed about the exterior of the construction "lot" or zone 12. Accordingly, the terrain is graded down to the existing level 13 of lot 12.

Subsequently, a diaphragm wall 14 of a type which is impervious to fluid and which is to be stabilized in its upstanding position is disposed upright in the ground 16. A suitable wall construction for this purpose may, for example, be a sheet-pile wall or, if the wall 14 is to become a permanent portion of the building structure to be erected on the site of the construction zone 12, it may be a slurry trench wall of the type, for example, as disclosed in U.S. Pat. No. 3,412,562. Each of the foregoing types of walls form an impervious fluid diaphragm satisfactory for the present method.

Wall 14 serves to complete the impervious boundary wall extending about the construction site 12 to the extent needed. Thus, for example, where one side of the construction site 12 is bounded by substantially impervious terrain 17, the construction site 12 can be enclosed by providing the sheet-pile walls to extend about three sides of the site 12.

' On the other hand, where no substantially impervious terrain is available, the construction site can be completely enclosed by walls 14.

The placement of walls 14 into the earth is done in a manner to permit the upper end of the walls to extend above the level of the surface 13 of the construction site 12. Thus, the upper edge of walls 14 enclosing site 12 form the rim of the construction zone boundaries and define a basin located above the level of the surface 13.

In order to provide a suitable location within construction site 12 from which to work and conduct the construction acthe inner faceof wall 14 and may suitably be anchored at its interior end by a conventional deadman or other anchor device 21. Thus, strut 19 serves to provide means serving to provide lateral support to the upper end of wall 14. It will be readily evident that other means such as the use of conventional tie-back devices may also be employed to introduce support to the upper end of wall 14 as desired and as feasible under the circumstances.

Pursuant" to the above preliminary steps, piles 22 may be driven into the earth for purposes of later providing support to a concrete mat 23. The driving of piles 22 can be accomplished by use of the driving extensions commonly employed in driving deep piles into the ground.

Next, basin 24 which was originally defined between the upper extension 14a of wall 14 and berm l8 and which included a bottom defined by the existing surface 13 of the construction site is filled with a heavy liquid, hereinafter referred to as a brine."

The brine" must not adversely coat the stabilizing fill material, such as sand, which will later replace the unstable material to be excavated out of the construction site. Thus, the "brine should not cause the normally stabilizing material to become unstable by virtue of contact with the liquid brine. In addition, the "brine preferably should be heavier than water since its purpose is to apply a supplemental hydrostatic pressure acting with passive resistance and/or strut forces acting against the wall from within the excavation site. Thus, the inside forces approximate the forces acting from outside. Conditions inany given circumstance will serve to dictate the degree of supplemental hydrostatic pressure required to properly hold the wall.

In one particularly preferred application, the brine" solution employed consists of a liquid having a density running on the order of 75 'lbs. per cubic foot as compared to the conventional weight of water. In order to prepare suitable brine solution, sodium chloride, calcium chloride, zinc chloride,

sodium silicate, or mixtures of various other materials can be relatively high internal friction angle as compared to the internal friction angle of that material 16 which was removed from basin 24, is introduced. Thus, in FIG. 4, sand 27 is shown having been filled into the excavation as a replacement for the material 16 which has been previously removed. During this manipulation, the level 28 of the brine" is maintained substantially constant so as to insure that the head of pressure applied against the inside of wall 14 remains throughout the interchange of stable material for the unstable material being removed.

Subsequently, substantially all of the brine is drained from the stable soil material 27 by means of pumps 29 and hoses 31 or the like.

If necessary, as for extremely deep holes or other conditions requiring greater strength than provided by the usual normal fill materials, such as sand, the internal friction angle of the fill material can be enhanced by reacting materials with the brine residue so as to cause crystal growth, solidification,

etc., thereby further increasing the internal friction angle of the fill and hence improving the stabilization property of the fill material.

In addition, portions (or all) of the stabilizedfill may be further strengthened by intrusions of special reacting or cementing materials or special tremie placements of cementitious mixtures.

After having drained the brine from the fill material27, the strut 19 can, if desired, be removed and further excavation conducted down to a level exposing the tops of piles 22. At that point, a layer 32 of good rock is placed around the tops of the piles 22 whereby a concrete mat 23 can be formed on the tops of piles 22. Mat 23 preferably can include a tapered or bevelled edge 33 against which a strut 34 can be positioned. The other end of strut 34 can then be attached near the upper edge of wall 14 in a manner to provide support between wall 14 and mat 23.

Subsequently, further excavation proceeds down through the sand 27 (or other stable material) placed into basin 24 until the only remaining stable material within the basin 24is that which lies below the level of the bottom of mat 23. This remaining rnat portion 27a (FIG. 8) is then graded level with the layer 32 of rock whereby additional concrete mat 36 can be formed between wall 14 and mat 23. Thus,lateral support is provided to the bottom end of wall 14 to counteract the inwardly pressing forces acting against the exterior of wall 14 at the lower end. In this manner, the lower end of wall 14 is 1 securely stabilized.

added to water together with other desirable materials such as dispersing agents, suspensions, or the like. Thus, the use of the term brine" is not to be limited herein merely to the use of salt water since a number of suitable ways of increasing the density will be readily apparent to those skilled in the art.

After filling the basin 24 with the brine," it will be readily apparent that the supplemental hydrostatic pressure on the inside of the wall essentially contributes to the support force countering the support forces acting on the outside of the wall. Then, while maintaining the supplemental hydrostatic pressure within the construction site 12, the unstable soil materials 16 are excavated from the construction site, or zone, down to a predetermined desired level 26. For example, this level 26 can advantageously be located on the order of 10 feet below the bottom of the structure to be built on the construction site. As noted above, during the excavation of the unstable materials 16 from the basin 24, the hydrostatic head" is maintained therein by merely supplying additional brine" material as desired by suitable means (not shown).

From the foregoing, it will be apparent that the volume of the fill material 27 is sufficient to stand alone in providing sufficient stability to the lower end of the wall to permit the construction of the rest of the foundation to proceed as where the concrete mat 23 is then subsequently laid taking advantage of the stable block of material 27a then located at the base of wall 14. Once mat 23 has been laid, it is then possible to utilize struts cooperating with mat 23 and wall 14 at various levels to counteract inwardly pressing forces acting against the wall while the concrete of mat 36 is being poured and permitted to harden.

From the foregoing, it is also readily apparent that during one stage of the proceedings there is provided a construction wall structure in an unstable footing wherein the stabilized wall construction comprises means forming an upright diaphragm wall, unstable footing material being located on oneside of the wall at the lower end thereof while a mat or block of stable footing material on the other side'of the wall has been deposited. Further, a mat of concrete is superimposed upon the first named mat and serves to counteract laterally acting forces pressing against the outside of the wall.

Thus, the portion 270 forms a mat of stable footing material upon which the mat 36 of concrete can be applied.

In operation, the method described above serves to keep the walls 14 of the construction site from losing their support notwithstanding the fact that they are lodged in an unstable soil material.

I claim:

disposed further away from said wall than the first named said mat and at a distance from said wall to permit struts to extend therefrom to engage the wall for supporting same, both said mats being disposed on the same side of said wall, and piles supporting said second mat of concrete. 

1. In a stabilized wall construction in an unstable footing, means forming an upright diaphragm wall, unstable footing material on one side of the wall at the lower end thereof, a deposit of stable footing material substituted for unstable material on the other side of the wall, a mat of concrete supported by said deposit serving to counteract laterally acting forces pressing against said one side, a second mat of concrete disposed further away from said wall than the first named said mat and at a distance from said wall to permit struts to extend therefrom to engage the wall for supporting same, both said mats being disposed on the same side of said wall, and piles supporting said second mat of concrete. 